U.S. Pat. No. 5,322,055 describes an ultrasonic surgical apparatus which includes a surgical instrument having a handpiece with a transducer for converting an electrical signal into longitudinal vibratory motion. The longitudinal vibratory motion is transmitted to an ultrasonic blade which is connected to the handpiece. An accessory is releasably connected to the handpiece to enable clamping of tissue against the vibrating blade to afford improved coagulating and cutting of tissue. In U.S. Pat. No. 5,322,055 Scissors-like grips actuate a pivoted clamp jaw along one side of the ultrasonically vibrating blade to compress and bias tissue against the blade in a direction which is substantially normal to the direction of longitudinal vibratory movement. In U.S. Pat. No. 5,322,055, the clamp jaw and blade are rotatable relative to one another to align a selected blade edge of a multi-edged blade with the clamp jaw for cutting and coagulating while clamping or circumferentially spacing a selected blade edge from the clamp jaw for cutting and coagulating without clamping. U.S. Pat. No. 5,322,055 is hereby incorporated herein by reference.
Many surgical instruments, such as the ultrasonic surgical device illustrated and described in U.S. Pat. No. 5,322,055, use elements such as actuation rods to transmit force from the proximal end of the instrument, where the instrument is gripped by the surgeon, to the distal end of the instrument where the transmitted force is used to actuate an end effector such as, for example, a clamping jaw. In order to effectively transmit force from the surgeons hand to the end effector in such an instrument, it is necessary to translate the grasping motion of the surgeons fingers to the lateral motion of the actuation rod. Scissors type grips are used in many surgical devices of this kind because they are comfortable and tend to be familiar to the surgeon. Many such instruments use a single pivot pin in combination with a cam of some type to translate the arcuate motion of the scissor grip to the linear motion of the actuation rod. However, in certain circumstances, such an arrangement may not be acceptable, such as, for example, where the room in the instrument body is limited and rotational movement of the grip around a fixed pivot pin requires too much of the available room. Further, in order to increase the stroke in pivot pin arrangement, it is generally necessary to increase the distance from the pivot pin to the cam, requiring more room if a longer stroke is desired. It would, therefore, be advantageous to provide an improved actuation mechanism for translating the grasping motion of a human hand to the lateral motion necessary to drive an actuation rod. In particular, it would be advantageous to provide such an improved actuation mechanism without using a fixed pivot pin type arrangement. It would also be advantageous to provide such an improved actuation mechanism in an in line handle arrangement and to reduce the room necessary for the actuation mechanism without substantially reducing the stroke length of the actuation rod.